We are running HTML validators as part of an effort to attain WCAG 2.0 A compliance.
Among the errors we are seeing is
The summary attribute is obsolete. Consider describing the structure of the table in a caption element or in a figure element containing the table; or, simplify the structure of the table so that no description is needed.
Here is a snippet of the failing HTML, apparently from the rendering of the RadSocialShare control:
<div id="ctl00_TemplateBody_WebPartManager1_gwpciNewSocialShareCommon_ciNewSocialShareCommon_RadSocialShare1_compactPopup_C_comboBox" class="RadComboBox RadComboBox_Default" style="width:160px;">
<table summary="combobox" border="0" style="border-width:0;border-collapse:collapse;">
We are currently running version 2013.2.717.45 of the ASP .NET for AJAX controls, but we just tried 2013.3.1015.45 and it didn't fix things in this regard, either.
There is a similar discussion at http://www.telerik.com/community/forums/aspnet-ajax/combobox/table-summary-attribute.aspx , which recommends a jQuery fix. This fix works in terms of removing the summary attribute from that table, but it does not result in clean HTML when the w3c validator is run against it, so we believe that is not an acceptable workaround.
In the discussion at http://www.telerik.com/community/forums/aspnet-ajax/general-discussions/accessibility-issues-various.aspx , some mention is made of fixing the combo box for the 2012 Q3 release, but it doesn't look like that happened.